[PATCH v2 10/10] KVM: Pre-check uaccesses in KVM's APIs to read/write guest memory
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COOLING7d
From: Sean Christopherson <seanjc@google.com>
Date: 2026-10-01 20:22:58
Also in:
kvm, lkml
Subsystem:
kernel virtual machine (kvm), the rest · Maintainers:
Paolo Bonzini, Linus Torvalds
Add a check on whether or not doing a user access is ok in KVM's APIs for
accessing guest memory, *before* doing memslot lookup/validation, so that
buggy KVM accesses to guest memory more likely to fail noisily. Because
KVM installs dummy/empty memslots early in VM destruction, bugs in the VM
teardown path will fail on the memslot checks without getting to the WARNs
buried in kvm_copy_{to,from}_user() and friends.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
virt/kvm/kvm_main.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 770a2c3bd445..80b19d47840b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c@@ -3211,6 +3211,11 @@ static int next_segment(unsigned long len, int offset) return len; } +static bool kvm_is_guest_access_ok(struct kvm *kvm, int offset, int len, int size) +{ + return kvm_can_do_uaccess(kvm) && !WARN_ON_ONCE(offset + len > PAGE_SIZE); +} + /* Copy @len bytes from guest memory at '(@gfn * PAGE_SIZE) + @offset' to @data */ static int __kvm_read_guest_page(struct kvm *kvm, struct kvm_memory_slot *slot, gfn_t gfn, void *data, int offset, int len)
@@ -3218,7 +3223,7 @@ static int __kvm_read_guest_page(struct kvm *kvm, struct kvm_memory_slot *slot, int r; unsigned long addr; - if (WARN_ON_ONCE(offset + len > PAGE_SIZE)) + if (!kvm_is_guest_access_ok(kvm, offset, len, PAGE_SIZE)) return -EFAULT; addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
@@ -3294,7 +3299,7 @@ static int __kvm_read_guest_atomic(struct kvm *kvm, struct kvm_memory_slot *slot int r; unsigned long addr; - if (WARN_ON_ONCE(offset + len > PAGE_SIZE)) + if (!kvm_is_guest_access_ok(kvm, offset, len, PAGE_SIZE)) return -EFAULT; addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
@@ -3327,7 +3332,7 @@ static int __kvm_write_guest_page(struct kvm *kvm, int r; unsigned long addr; - if (WARN_ON_ONCE(offset + len > PAGE_SIZE)) + if (!kvm_is_guest_access_ok(kvm, offset, len, PAGE_SIZE)) return -EFAULT; addr = gfn_to_hva_memslot(memslot, gfn);
@@ -3457,7 +3462,7 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc, int r; gpa_t gpa = ghc->gpa + offset; - if (WARN_ON_ONCE(len + offset > ghc->len)) + if (!kvm_is_guest_access_ok(kvm, offset, len, ghc->len)) return -EINVAL; if (slots->generation != ghc->generation) {
@@ -3495,7 +3500,7 @@ int kvm_read_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc, int r; gpa_t gpa = ghc->gpa + offset; - if (WARN_ON_ONCE(len + offset > ghc->len)) + if (!kvm_is_guest_access_ok(kvm, offset, len, ghc->len)) return -EINVAL; if (slots->generation != ghc->generation) {
--
2.56.0.rc1.315.gc6ed9934b7-goog